From b3d14bff12a38ad13a174eb0cc83d2ac7169eee4 Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Wed, 10 Nov 2010 21:21:35 +0100 Subject: dccp ccid-2: Implementation of circular Ack Vector buffer with overflow handling This completes the implementation of a circular buffer for Ack Vectors, by extending the current (linear array-based) implementation. The changes are: (a) An `overflow' flag to deal with the case of overflow. As before, dynamic growth of the buffer will not be supported; but code will be added to deal robustly with overflowing Ack Vector buffers. (b) A `tail_seqno' field. When naively implementing the algorithm of Appendix A in RFC 4340, problems arise whenever subsequent Ack Vector records overlap, which can bring the entire run length calculation completely out of synch. (This is documented on http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/\ ack_vectors/tracking_tail_ackno/ .) (c) The buffer length is now computed dynamically (i.e. current fill level), as the span between head to tail. As a result, dccp_ackvec_pending() is now simpler - the #ifdef is no longer necessary since buf_empty is always true when IP_DCCP_ACKVEC is not configured. Signed-off-by: Gerrit Renker --- net/dccp/ackvec.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'net/dccp/ackvec.h') diff --git a/net/dccp/ackvec.h b/net/dccp/ackvec.h index 3e894a0173a7..23880be8fc29 100644 --- a/net/dccp/ackvec.h +++ b/net/dccp/ackvec.h @@ -21,6 +21,7 @@ * the maximum size of a single Ack Vector. Setting %DCCPAV_NUM_ACKVECS to 1 * will be sufficient for most cases of low Ack Ratios, using a value of 2 gives * more headroom if Ack Ratio is higher or when the sender acknowledges slowly. + * The maximum value is bounded by the u16 types for indices and functions. */ #define DCCPAV_NUM_ACKVECS 2 #define DCCPAV_MAX_ACKVEC_LEN (DCCP_SINGLE_OPT_MAXLEN * DCCPAV_NUM_ACKVECS) @@ -55,8 +56,10 @@ static inline u8 dccp_ackvec_state(const u8 *cell) * @av_buf_head: head index; begin of live portion in @av_buf * @av_buf_tail: tail index; first index _after_ the live portion in @av_buf * @av_buf_ackno: highest seqno of acknowledgeable packet recorded in @av_buf + * @av_tail_ackno: lowest seqno of acknowledgeable packet recorded in @av_buf * @av_buf_nonce: ECN nonce sums, each covering subsequent segments of up to * %DCCP_SINGLE_OPT_MAXLEN cells in the live portion of @av_buf + * @av_overflow: if 1 then buf_head == buf_tail indicates buffer wraparound * @av_records: list of %dccp_ackvec_record (Ack Vectors sent previously) * @av_veclen: length of the live portion of @av_buf */ @@ -65,7 +68,9 @@ struct dccp_ackvec { u16 av_buf_head; u16 av_buf_tail; u64 av_buf_ackno:48; + u64 av_tail_ackno:48; bool av_buf_nonce[DCCPAV_NUM_ACKVECS]; + u8 av_overflow:1; struct list_head av_records; u16 av_vec_len; }; @@ -112,9 +117,10 @@ extern int dccp_ackvec_parse(struct sock *sk, const struct sk_buff *skb, const u8 *value, const u8 len); extern int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seq, u8 sum); +extern u16 dccp_ackvec_buflen(const struct dccp_ackvec *av); -static inline int dccp_ackvec_pending(const struct dccp_ackvec *av) +static inline bool dccp_ackvec_is_empty(const struct dccp_ackvec *av) { - return av->av_vec_len; + return av->av_overflow == 0 && av->av_buf_head == av->av_buf_tail; } #endif /* _ACKVEC_H */ -- cgit v1.2.3